Honey Bee Enemy #1: Varroa Mites

Honey bees pollinate about 1/3 of the human diet, directly or indirectly to apples, blueberries, and 130 other crops in the United States. For fruit and nut crops, the degree of pollination dictates the maximum yield and profitability of these crops. This is why bee pollination services are reported at $9 billion plus within the United States alone.

Valuable bee populations have risen and fallen within the past decade due to numerous causes. Some report that the honey bee’s worst enemy is man with improper use of insecticides. However I disagree. We propagate bees, promote their good genes, aid their health against natural diseases, and supply them with abundant foraging acreage in a mutual beneficial relationship. Enemy # 1 is debatable, but Varroa destructor, a mite (below arrow above) rate very high on the list. The worst enemy is the one in a beekeeper’s hive.

Varroa mites actually originated in Asia. There they did little harm to the eastern honey bees. But when American honey bees were brought to Asia, the devastating damage to hives became evident. Then over the past 100 years, these mites have spread worldwide.

A Varroa mite (under blue arrow) attacking a juvenile honey bee

The adult mites are reddish brown, round, and range from one to two millimeters in diameter. Varroa go between the bee segments, puncture the soft tissue, and feed on bee hemolymph through the puncture. The mites are passed from bee to bee in the hive. Also they are transported to other hives when bees drift into other hives, when healthy bees rob weaker hives, and when beekeepers put hives in new locations.

When the mites reproduce, they enter the brood cells of larval bees that are about to be capped. The mites feed on the bee larvae, lay eggs that soon hatch, and both continue to feed on the bee larvae. The result of this feeding is damage or death to the developing bee. It is safe to assume that hundreds of thousands of bee hives have been destroyed, causing billions of dollars of economic loss.

It sounds hopeless, but beekeepers can take countermeasures. Sticky traps underneath a screen bottom tray can capture the varroa mites as they frequently fall off the bees. Placing colonies in full sun modestly reduce varroa numbers. Fogging mineral oil and dusting the bees with powdered sugar have not been proven to be effective to this date.

The most significant advancement toward control has been through genetic breeding programs. Favored genes are associated with bee behavior. One behavior is for the bees to groom themselves and other bees in the brood. Therefore mites are knocked off the bees lowering the mites in the bee colony. Another behavior is hygienic bees that can detect problems in the developing brood. They uncapped the infected larvae and remove it from the hive. This hygienic behavior is called ‘varroa sensitive hygiene’ or simply ‘VSH’. Bees with these genetic traits can be purchased from specific bee suppliers.

Contact Keith Hawkins (337-463-7006) at the LSU Agcenter or the Southwest Beekeeper’s Association for additional information.